1. Field of the Invention
The present invention relates to a method of producing a thin film grown on a semiconductor substrate.
2. Related Art
For example, in a case where a silicon raw material gas is fed in a reaction vessel of a thin film growth apparatus for the purpose of growing a silicon single crystal thin film on a silicon single crystal substrate, silicon is deposited unintentionally on the surface exposed to the atmosphere in the vessel, such as an inner wall of the vessel, a holder for holding a silicon single crystal substrate, a gas nozzle, and the other jigs as well as on a main surface of the substrate.
Part of deposit having the shapes of a particulate or a flake formed in the reaction vessel is frequently peeled during the growth of a thin film and some of the peeled debris comes to attach on a semiconductor substrate. The debris on the substrate causes anomalous part in the thin film, such as stacking faults or protruding defects. A cleaning operation, therefore, has been required regularly to remove the deposit in the vessel.
As a function for eliminating the deposit, an aqueous solution of a strong acid or a strong base has been used to eliminate the deposit in the reaction vessel of a thin film growth apparatus through the etching action. In the case of silicon as the deposit, for example, a strong acid such as an aqueous mixture solution of hydrofluoric acid and nitric acid is used. Such an etching method by using the aqueous solution requires an operation for dismantling a reaction vessel, a holder for a substrate, a gas nozzle and the other jigs from the thin film growth apparatus to clean them, since the method is carried out in a wet condition. The wet etching method cannot be frequently applied for eliminating the deposit in the reaction vessel, since it consumes much time in such operations as dismantling, assembling, and restarting up the apparatus after adjusting the operative condition.
Another method for elimination of the deposit in the reaction vessel widely known is to introduce hydrogen chloride gas into the reaction vessel kept at a temperature near 1200.degree. C. in order to etching off the deposit after unloading a semiconductor substrate on which a thin film has been grown.
In the case where hydrogen chloride gas is introduced into the reaction vessel at such a high temperature, however, members in the vessel suffers from damages and the reaction area is contaminated by metals carried on the hydrogen chloride gas stream.
When a thin film growth apparatus of cold-wall type is used, there are also problems that various kinds of contaminants present in non-heated regions, such as the wall, of relatively low temperature in the reaction vessel, are difficult to be removed by the use of hydrogen chloride gas, and contaminants once etched off at high temperature regions come to be again deposited on the non-heated regions and mixed into growing thin films by revaporization, which will result in crystal quality degradation of the thin film.
In light of the above-mentioned problems in the conventional methods, new cleaning gases were proposed. In this case, gases of high reactivity are used at low temperature to clean the interior of the reaction vessel of the thin film growth apparatus, wherein a gas including at least one of the group consisting of ClF, ClF.sub.3, and ClF.sub.5 is used to eliminate deposit in the thin film growth apparatus, said deposit being a metal or compounds thereof (see published Japanese patent No. Sho 64-17857).
When a cleaning gas, C1F.sub.3 (chlorine trifluoride) is used for cleaning the interior of the reaction vessel containing a substrate holder made of graphite coated with SiC (silicon carbide), however, there happens a problem that the surface of the substrate holder is corroded by chlorine trifluoride, and in succession, the graphite in the holder is vigorously attacked and corroded to generate particulate. Consequently, the method for cleaning the interior of a reaction vessel by the use of ClF.sub.3 has not been put into practical use.
Silicon carbide has been used was black in color and non-transparent even though it is obtained as a simple substance in the market. It means imbalanced stoichiometry in composition between carbon and silicon, thus either silicon or carbon is partly segregated in the solid not being sited at the lattice. It is believed by the inventors that the segregated silicon or carbon is preferably attacked by chlorine trifluoride used as a cleaning gas.